Skin‐Like Tri‐Modal Sensors Based on Soft Piezoelectric and Ionic Composites

It was recently shown that acute respiratory distress syndrome (ARDS) mortality has not been reduced in over 15 years and remains ~40 %, even with protective low tidal volume (LVt) ventilation. Thus, there is a critical need to develop novel ventilation strategies that will protect the lung and reduce ARDS mortality. Protti et al. have begun to analyze the impact of mechanical ventilation on lung tissue using engineering methods in normal pigs ventilated for 54 h. They used these methods to assess the impact of a mechanical breath on dynamic and static global lung strain and energy load. Strain is the change in lung volume in response to an applied stress (i.e., Tidal Volume-Vt). This study has yielded a number of exciting new concepts including the following: (1) Individual mechanical breath parameters (e.g., Vt or Plateau Pressure) are not directly correlated with VILI but rather any combination of parameters that subject the lung to excessive dynamic strain and energy/power load will cause VILI; (2) all strain is not equal; dynamic strain resulting in a dynamic energy load (i.e., kinetic energy) is more damaging to lung tissue than static strain and energy load (i.e., potential energy); and (3) a critical consideration is not just the size of the Vt but the size of the lung that is being ventilated by this Vt. This key concept merits attention since our current protective ventilation strategies are fixated on the priority of keeping the Vt low. If the lung is fully inflated, a large Vt is not necessarily injurious. In conclusion, using engineering concepts to analyze the impact of the mechanical breath on the lung is a novel new approach to investigate VILI mechanisms and to help design the optimally protective breath. Data generated using these methods have challenged some of the current dogma surrounding the mechanisms of VILI and of the components in the mechanical breath necessary for lung protection.

Bone is constantly exposed to dynamic and static loads, which induce both dynamic and static bone strains. Although numerous studies exist on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain needs further investigation. Therefore, the effect of two different static bone strain levels on implant stability and bone remodeling at two different implantation times was investigated in a rabbit model. Two different test implants with a diametrical expansion of 0.15 mm (group A) and 0.05 mm (group B) creating initial static bone strains of 0.045 and 0.015, respectively. The implants were inserted in the proximal tibial metaphysis of 24 rabbits to observe the biological response at implant removal. Both groups were compared to control implants (group C), with no diametrical increase. The insertion torque (ITQ) was measured to represent the initial stability and the removal torque (RTQ) was measured to analyze the effect that static strain had on implant stability and bone remodeling after 3 and 13 days of implantation time. The ITQ and the RTQ values for test implants were significantly higher for both implantation times compared to control implants. A selection of histology samples was prepared to measure bone to implant contact (BIC). There was a tendency that the BIC values for test implants were higher compared to control implants. These findings suggest that increased static bone strain creates higher implant stability at the time of insertion, and this increased stability is maintained throughout the observed period.

The effects of applied strain on sealants exposed to outdoor weathering were examined for two sealant formulations, Sealants A and C. Both static and dynamic strain was applied to the sealants during the summer in a Gaithersburg, MD outdoor location. Both sealants exhibited a reversible change in equilibrium distance. Stress relaxation studies on all samples revealed that, for Sealant A, two mechanisms affected modulus change; exposure without applied strain increased the modulus while additionally applied strain decreased the modulus. Only one mechanism that decreased the modulus was found for Sealant C. A 7 % dynamic strain and a 25 % static strain were observed to produce equivalent modulus changes in both systems.

Measurements of the yield points ΔσA on reloading after ageing at various stress levels (obtained by partial unloading of the tensile specimen) have been performed with Cu-2at.% Mn polycrystals at 313K (strain rate 310−5s−1). At these temperatures solute atoms are supposed to increase the effective obstacle strength (intersections of mobile with forest dislocations) by pipe diffusion from the forest to the mobile dislocations during the waiting time for thermal activation. The stress dependence ΔσA ∝ (σ*)1/3, (with the effective stress σ*) expected according to Friedel's equation is observed. This supports the intersection strengthening model and, hence, the pipe diffusion mechanism for static and dynamic strain ageing in the temperature and strain rate regime of this study.

Combined measurements of shear stress relaxation and differential dynamic storage and loss shear moduli G′ and G″ have been made on styrene-butadiene rubber (type 1502) containing 50 phr N299 carbon black and 10 phr Sundex 790 oil, both cured and uncured, and compared with similar measurements on the cured and uncured gum rubber. The range of temperature was −22.5° to 63°C, and of static shear strain 0.01 to 0.40; the maximum oscillatory shear strain was about 0.005 and the frequency was usually 0.64 Hz. Dynamic measurements of G′ and G″ with no superposed static strain and stress relaxation measurements at small strains on the filled samples could be reduced by frequency-temperature superposition with αT shift factors that were somewhat larger than those that applied to the raw or crosslinked gum. At about 0.6 Hz, the filler increased the storage modulus by about a factor of 5 for the cured sample and about 10 for the uncured; the moduli for the cured and uncured filled samples were almost identical. The order of rates of relaxation was unfilled uncured > filled uncured > filled cured > unfilled cured. At small static strains, the stress relaxation of the filled samples (both uncured and cured) was substantial, but the differential dynamic moduli G′ and G″ remained nearly equal to their values with zero static strain throughout the relaxation process. With increasing static strain γ, the strain-dependent relaxation modulus G(γ;t) decreased by as much as a factor of 3 for the filled, cured sample and 4 for the filled, uncured sample. The modulus G(γ;t) could not be factored into a strain-dependent and a time-dependent function. During stress relaxation of the filled samples (both cured and uncured) at large strains, the differential storage modulus G′(ω,γ;t) experienced a drop followed by slow recovery toward its initial value at 25°C; the loss modulus G″(ω,γ;t) was unchanged. For the filled, cured sample, complete recovery to the initial value G′(ω,0) (where 0 refers to zero static strain) was accomplished by removing the shearing stress and heating for one day at 63° followed by return of the temperature to 25°C. The results are interpreted in terms of a structure which combines a crosslinked (or, in the case of uncured, an entangled) polymer network and a network of carbon black particles. At small strains, stress relaxation is thought to be accomplished primarily by rearrangements of carbon particles and/or polymer molecules bridging them, without structural damage in the sense that the rearranged structure has the same properties as the original. These rearrangements are impeded by crosslinking in the cured vis-a-vis the uncured filled rubber. The kinetics of rearrangement may be governed by configurational changes of the polymer molecules since the temperature shift factors do not differ greatly from those for the gum rubber. At large strains, the particle network can be damaged but can regain its structure by a healing process which is accelerated at higher temperatures. The conclusions apply to the particular compound studied here and not necessarily to other rubber-black compounds, which according to the literature show great diversity of properties.

Dynamic power cables used in floating offshore renewable energy systems are subjected to continuous mechanical strain from hydrodynamic forces, making insulation reliability a critical design consideration. Current qualification standards predominantly rely on sequential testing of mechanical and electrical properties, which may overlook degradation mechanisms arising from their interaction under real-world conditions. This study presents a novel in-situ approach that combines electrical, mechanical and optical monitoring and testing of cross-linked polyethylene (XLPE) cable specimens, under strain conditions representative of dynamic offshore environments. In contrast to previous studies that examined only static strain, the present work investigates cyclic tensile loading to capture the coupled effects of time-varying mechanical strain and electrical energization. Five samples per condition were subjected to cyclic tensile strain amplitudes up to 2.8% at frequencies of 0.05, 0.1, and 0.2 Hz, under a 50 Hz AC voltage of 7.5 kVrms. Results demonstrate that dynamic strain accelerates tree growth and narrows final electrical tree geometries, height-width ratios doubled under dynamic conditions. Static tensile strain significantly shortens the initiation time and time-to-failure from an average of 306 down to 155 minutes. When comparing samples that were tested sequentially, similar breakdown characteristics were observed with subtle differences in tree morphology and propagation characteristics. These findings confirm that sequential testing does not fully replicate the degradation behavior observed under simultaneous loading. This work underscores the need for rigorous combined electro-mechanical testing when evaluating new cable materials and designs intended for dynamic applications in floating offshore wind.

This article presents evidence for the channeling of strain energy released by the Ms = 7.4 Landers, California, earthquake within the eastern California shear zone (ECSZ). We document an increase in seismicity levels during the 22-hr period starting with the Landers earthquake and culminating 22 hr later with the Ms = 5.4 Little Skull Mountain (LSM), Nevada, earthquake. We evaluate the completeness of regional seismicity catalogs during this period and find that the continuity of post-Landers strain release within the ECSZ is even more pronounced than is evident from the catalog data. We hypothesize that regional-scale connectivity of faults within the ECSZ and LSM region is a critical ingredient in the unprecedented scale and distribution of remotely triggered earthquakes and geodetically manifest strain changes that followed the Landers earthquake. The viability of static strain changes as triggering agents is tested using numerical models. Modeling results illustrate that regional-scale fault connectivity can increase the static strain changes by approximately an order of magnitude at distances of at least 280 km, the distance between the Landers and LSM epicenters. This is possible for models that include both a network of connected faults that slip “sympathetically” and realistic levels of tectonic prestrain. Alternatively, if dynamic strains are a more significant triggering agent than static strains, ECSZ structure may still be important in determining the distribution of triggered seismic and aseismic deformation.

A robust ceramic strain gage has been developed for propulsion health monitoring which is capable of measuring both static and dynamic strains at temperatures up to 1400/spl deg/C. These thin film sensors are ideally suited for in-situ strain measurement in harsh environments such as those encountered in the hot sections of gas turbine engines. The sensors are non-intrusive and robust enough to withstand the high g loading associated with rotating engine components. Since gage thickness is considerably less than the boundary layer thickness, these sensors do not adversely affect the gas flow path through the engine. Results of recent laboratory tests have shown that these strain gages can meet many of the current demands of high performance propulsion engines. Specifically, static strain tests have been performed at temperatures as high as 1400/spl deg/C, which have resulted in a relatively large and reproducible piezoresistive response. In addition, high frequency dynamic strain tests were performed at temperatures up to 500/spl deg/C and at frequencies up to 2000 Hz to simulate conditions that would be encountered during high cycle fatigue. The results indicated that not only did these sensors survive severe testing conditions, including an applied strain of /spl plusmn/500 /spl mu//spl epsiv/, but that they were sensitive enough to isolate possible causes of high cycle fatigue. The results of both the static and dynamic strain measurements at elevated temperature using these ceramic strain gages are presented and the prospects of using these strain gages for structural health monitoring are discussed.

Bone is known to adapt to the prevalent strain environment while the variation in strains, e.g., due to mechanical loading, modulates bone remodeling, and modeling. Dynamic strains rather than static strains provide the primary stimulus of bone functional adaptation. The finite element method can be generally used for estimating bone strains, but it may be limited to the static analysis of bone strains since the dynamic analysis requires expensive computation. Direct in vivo strain measurement, in turn, is an invasive procedure, limited to certain superficial bone sites, and requires surgical implementation of strain gauges and thus involves risks (e.g., infection). Therefore, to overcome difficulties associated with the finite element method and the in vivo strain measurements, the flexible multibody simulation approach has been recently introduced as a feasible method to estimate dynamic bone strains during physical activity. The purpose of the present study is to further strengthen the idea of using the flexible multibody approach for the analysis of dynamic bone strains. Besides discussing the background theory, magnetic resonance imaging is integrated into the flexible multibody approach framework so that the actual bone geometry could be better accounted for and the accuracy of prediction improved.

Al effects on strain aging and resistance against hydrogen embrittlement were examined in Fe–18Mn–0.6C-based twinning-induced plasticity steels deformed at different strain rates. These steels showed a hydrogen-induced fracture when they were pre-deformed at a strain rate of 1.7×10–6 s–1. This fracture was suppressed by increasing the strain rate and Al content. The two important factors for improving the resistance to hydrogen embrittlement from the viewpoint of material strengthening by strain aging were found to be (1) the suppression of dynamic strain aging by increasing the strain rate and Al content, and (2) the suppression of static strain aging under loading by the Al addition.

Mechanical power estimates the amount of energy delivered to ventilated lungs but there are no available data in neonates. We aim to provide a real-world description of power and investigate its relationship with clinical variables in neonates. Cross-sectional study enrolling neonates of any gestational age. Patients were classified as recovering from respiratory distress syndrome (RDS), affected by neonatal acute respiratory distress syndrome (ARDS), or with evolving broncho-pulmonary dysplasia (BPD). Simultaneously collected ventilation and oxygenation data as well as ultrasound-assessed lung aeration were used; power was calculated with four different equations. 100 (55 males) neonates (32 with RDS, 30 with neonatal ARDS, 10 with evolving BPD and 28 controls with no lung disease) were studied. Distributions of power and energy (i.e. power for a single breath) for the whole population were given (median power ranging between 0.28 [0.18, 0.39] and 0.39 [0.29, 0.54] J/min/Kg, median energy ranging between 7.1 [4.9, 9.1] and 9.5 [6.8, 12.3] mJ/Kg). Median power (difference varying between 0.21 and 0.9 J/min/Kg (p always <0.001), depending on the used equation) and energy (difference varying between 0.9 and 3 mJ/Kg (p always <0.001), depending on the used equation) were higher in neonates with respiratory failure than in controls. Components of power due to dynamic and static strain showed similar differences. Power correlated with oxygenation (adj-ρ between 0.18 (95%CI: 0.02; 0.34) and 0.22 (95%CI: 0.06; 0.38), p varying between 0.032 and 0.045) and lung aeration impairment (ρ between 0.25 (95%: 0.07;0.41) and 0.27 (95%CI: 0.08; 0.43), p varying between 0.009 and 0.013, depending on the used equation). Mechanical power, its components due to dynamic and static strain, and energy are higher in neonates with respiratory disorders than in controls. Mechanical power and its components are correlated with impairment of oxygenation and lung aeration.

This paper is a part of research to develop convenient method for continuous monitoring of arterial blood pressure by non-invasive and non-oscillometric way. A simple optical method, using self-mixing in a diode laser, is used for detection of skin surface vibrations near the artery. These vibrations, which can reveal the pulsate propagation of blood pressure waves along the vasculature, are used for pulse wave registration. The registration of the Pulse Wave Transit Time (PWTT) is based on computing the time delay in different regions of the human body using an ECG as a reference signal. In this study, the comparison of method of optical self-mixing with other methods as photoplethysmographic (PPG) and bioimpedance (BI) for PWTT is done. Also correlation of PWTT, obtained with different methods, with arterial blood pressure is calculated. In our study, we used a group of volunteers (34 persons) who made the bicycle exercise test. The test consisted of cycling sessions of increasing workloads during which the HR changed from 60 to 180 beats per minute. In addition, a blood pressure (NIBP) was registered with standard sphygmomanometer once per minute during the test and all NIBP measurement values were synchronized to other signals to find exact time moments where the systolic blood pressure was detected (Korotkoff sounds starting point). Computer later interpolated the blood pressure signal in order to get individual value for every heart cycle. The other signals were measured continuously during all tests. At the end of every session, a recovery period was included until person's NIBP and heart rate (HR) normalized. As a result of our study it turned out that time intervals that were calculated from plethysmographic (PPG) waveforms were in the best correlation with systolic blood pressure. The diastolic pressure does not correlate with any of the parameters representing PWTT. The pulse wave signals measured by laser and piezoelectric transducer are very similar and do not have any qualitative differences. Since the detection of pulse wave by piezoelectric transducer is less complicated than laser detection, the piezo transducer should be preferred in such cases, but advantage of optical method of measurement is absent of any mechanical influence to artery.

The strain dependence of the dynamic mechanical properties of HAF‐N330‐filled EPDM vulcanizate was studied using a Rheovibron DDV III EP. It is shown that when a dynamic strain is superposed on a static strain, the viscoelastic response of filled rubbers becomes more complex. Under these conditions, dynamic mechanical properties do not correlate with the double strain amplitude. A strain called the “total strain” has been defined in order to interpret the experimental results. It is also shown that the dynamic mechanical properties are displacement velocity dependent, while the comparison is made under identical conditions of strain and frequency. Separability of time and strain effects is observed for the storage modulus, whereas the loss modulus is shown to be a nonseparable function. The elastic and the relaxation components, constituting the mixed function representing the storage modulus are shown to have similar deformation dependence. © 1994 John Wiley &amp; Sons, Inc.

We report on civil engineering applications of wavelength multiplexed optical fiber Bragg grating arrays directly produced on the draw tower for testing and surveying advanced structures and materials such as carbon fiber reinforced concrete elements and prestressing cables. We equipped a 6×0.9×0.5 m concrete beam, which was reinforced with carbon fiber reinforced epoxy laminates, and a 7‐m long prestressing carbon fiber cable made of seven twisted strands, with optical fiber Bragg grating sensors. Static strains up to 8000 <em>μ</em>m/m and dynamic strains up to 1200 <em>μ</em>m/m were measured with a Michelson interferometer used as Fourier spectrometer with a resolution of about 10 <em>μ</em>m/m for all sensors. Comparative measurements with electrical resistance strain gauges were in good agreement with the fiber optic results. We installed the fiber sensors in two different arrangements: some Bragg grating array elements measured local strain while others were applied in an extensometric configuration to measure moderate strain over a base length of 0.1 to 1 m.

This special section is dedicated to geophysical distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) applications. Since the introduction of commercial DTS units in the 1980s and more recent deployment of DAS in this decade, distributed sensing is quietly revolutionizing sectors of geophysics, particularly those requiring permanent downhole measurements. The common component of distributed sensing technologies is the use of laser scattering measurements on fiber-optic cables (tens of kilometers long) to estimate the physical state of each fiber segment with measurands including temperature (DTS), static strain (DSS), and, most recently, dynamic strain and seismic waves (DAS) recorded either continuously or on an as-needed basis. The high spatial coverage, accuracy, and resolution of this technology make it a truly groundbreaking addition to our subsurface sensing toolbox.